1. Field of Invention
The present disclosure relates generally to photo masks used in fabrication of semiconductor devices and more particularly to blank substrates for extreme ultraviolet (EUV) photo masks and fabricating an extreme ultraviolet (EUV) photo mask using the same.
2. Related Art
To accomplish greater degree of high integration, continuous reduction of the light wavelength in photolithography is imperative in order to improve the resolution of the patterns transferred to a semiconductor wafer. A photolithography apparatus utilizes lights such as the visible rays, ultraviolet (UV) rays, deep ultraviolet (DUV) rays, etc. The deep ultraviolet (DUV) rays were widely used as the source lights of the photolithography apparatus, because about 365 nanometers (nm), 248 nm, or 193 nm wavelengths of the deep ultraviolet (DUV) rays are relatively shorter than the wave lengths of the visible rays and the ultraviolet (UV) rays. In particular, the argon fluoride (ArF) lasers generating the DUV lights of about 193 nm wave length have been widely utilized in many photolithography apparatuses. However, the argon fluoride (ArF) lasers are not known to produce satisfactory results when transferring the fine patterns having the line widths of about 70 nm or the less to a wafer.
The immersion photolithography techniques using the ArF lasers have been proposed for purposes of improving the resolution of the patterns. The immersion photolithography techniques utilize an immersion liquid provided between the wafer and the lens module. Nevertheless, an effective photolithography technique for transferring the small patterns having the line widths of about 40 nm or the less are yet to be found. It is an on-going process to develop the next generation lithography (NGL) techniques that would transfer the fine and small patterns. Some examples of the next generation lithography (NGL) are the extreme ultraviolet (EUV) lithography techniques, the electron beam lithography techniques, the proximity electron beam lithography techniques, the proximity x-ray lithography techniques, and the ion beam lithography techniques. The EUV lithography techniques may utilize a light having of about 13 nm to about 14 nm wave length and an anisometric mirror optical system.